Reduction studies on mixed chelate complexes

Robert J. Balahura, Nita Lewis

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Abstract

The Cr2+ reductions of the complexes [Co(en)(ptdn)2]+, [Co(en)2(ptdn)]2+, and [Co(en)3]3+ have been studied. The reaction of [Co(en)(ptdn)2]+ proceeded by three pathways: inner-sphere monobridged (k25°C = (2.5 ± 0.2) × 10-3 M-1 s-1, ΔH = 13.7 ± 0.9 kcal mol-1, ΔS = -24 ± 3 eu), inner-sphere dibridged (k25°C = (2.1 ± 0.2) × 10-3 M-1 s-1, ΔH = 13 ± 1 kcal mol-1, ΔS = -28 ± 5 eu), and outer sphere (k25°C = (2.0 ± 0.2) × 10-3 M-1 s-1, ΔH = 10 ± 2 kcal mol-1, ΔS = -36 ± 7 eu); μ = 1.0 M (LiClO4). The [Co(en)2(ptdn)]2+ complex was reduced by Cr2+ with k50°C = 5.7 × 10-5 M-1 s-1, μ = 1.0 M (LiClO4). This reaction was shown to occur partially by an inner-sphere path. For [Co(en)3]3+ only an outersphere path is possible and k50°C = 1.1 × 10-4 M-1 s-1, μ = 1.0 M (LiClO4). Rate trends within the series [Co(ptdn)3], [Co(en)(ptdn)2]+, [Co(en)2(ptdn)]2+, and [Co(en)3]3+ as well as within the analogous oxalato-Co(III) complexes are discussed in terms of ligand field effects.

Original languageEnglish
Pages (from-to)4716-4721
Number of pages6
JournalJournal of the American Chemical Society
Volume99
Issue number14
StatePublished - Dec 1 1977
Externally publishedYes

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Ligands
tris(ethylenediamine)cobalt(III)
lithium perchlorate

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Reduction studies on mixed chelate complexes. / Balahura, Robert J.; Lewis, Nita.

In: Journal of the American Chemical Society, Vol. 99, No. 14, 01.12.1977, p. 4716-4721.

Research output: Contribution to journalArticle

Balahura, Robert J. ; Lewis, Nita. / Reduction studies on mixed chelate complexes. In: Journal of the American Chemical Society. 1977 ; Vol. 99, No. 14. pp. 4716-4721.
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abstract = "The Cr2+ reductions of the complexes [Co(en)(ptdn)2]+, [Co(en)2(ptdn)]2+, and [Co(en)3]3+ have been studied. The reaction of [Co(en)(ptdn)2]+ proceeded by three pathways: inner-sphere monobridged (k25°C = (2.5 ± 0.2) × 10-3 M-1 s-1, ΔH≠ = 13.7 ± 0.9 kcal mol-1, ΔS≠ = -24 ± 3 eu), inner-sphere dibridged (k25°C = (2.1 ± 0.2) × 10-3 M-1 s-1, ΔH≠ = 13 ± 1 kcal mol-1, ΔS≠ = -28 ± 5 eu), and outer sphere (k25°C = (2.0 ± 0.2) × 10-3 M-1 s-1, ΔH≠ = 10 ± 2 kcal mol-1, ΔS≠ = -36 ± 7 eu); μ = 1.0 M (LiClO4). The [Co(en)2(ptdn)]2+ complex was reduced by Cr2+ with k50°C = 5.7 × 10-5 M-1 s-1, μ = 1.0 M (LiClO4). This reaction was shown to occur partially by an inner-sphere path. For [Co(en)3]3+ only an outersphere path is possible and k50°C = 1.1 × 10-4 M-1 s-1, μ = 1.0 M (LiClO4). Rate trends within the series [Co(ptdn)3], [Co(en)(ptdn)2]+, [Co(en)2(ptdn)]2+, and [Co(en)3]3+ as well as within the analogous oxalato-Co(III) complexes are discussed in terms of ligand field effects.",
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